Boost pressure control, function

P09.40-2193-12

B5/1 Charge pressure sensor

B19/11 Temperature sensor upstream turbocharger
(with DPF code 474 as of12/2004)

B37 Accelerator pedal sensor

B60 Exhaust back pressure sensor (with DPF Code 474)

N3/9 CDI control unit

Y100/1 Right charge pressure positioner

Boost pressure control takes place according to the performance mapping of the boost pressure and the load request via the CDI control unit.

For the purpose of boost pressure control, the CDI control unit actuates the boost pressure positioner (according to its input signals).

The position of the guide vanes in the exhaust turbine is adjusted via the control linkage. The boost pressure is thus adapted to the temporary load status of the engine.

Engine and turbocharger protection (with DPF 474)

To prevent damage to the engine and the turbocharger due to overheating (if DPF is overloaded), the exhaust gas temperature upstream of the turbocharger (as of 12/2004) and the exhaust back pressure ( in the exhaust gas recirculation duct) are monitored.

If the exhaust back pressure is too high or the exhaust gas temperature too high, the CDI control unit reduces the boost pressure and the injection quantity to protect the turbocharger and the engine.

P09.40-2194-76

110/1 Control linkage

110/2 Guide vane

110/3 Turbine wheel

110a Exhaust gas turbine

110b Fresh air compressor

Y100/1 Right charge pressure positioner

a Flow cross-section

b Adjustment angle of guide vanes

A Boost pressure positioner actuated, guide vanes closed

B Boost pressure positioner not actuated, guide vanes opened

At low engine speeds, the guide vanes are closed increasingly and thus the flow cross-section reduced. As a result, the flow rate of the exhaust gas at the turbine wheel is increased, which in turn increases the speed of the turbine wheel and the compressor wheel. Thus the boost pressure and the engine torque are increased.

At high engine speeds, the guide vanes are opened increasingly and thus the flow cross-section increased. The desired boost pressure is obtained at a lower exhaust back pressure and fuel consumption thus reduced.